Feb 17, 2010

Listening to music over the 'net with authentication and cache

Having seen people really obsessed with the music, I don't consider myself to be much into it, yet I've managed to accumulate more than 70G of it, and counting. That's probably because I don't like to listen to something on a loop over and over, so, naturally, it's quite a bother to either keep the collection on every machine I use or copy the parts of it just to listen and replace.

Ideal solution for me is to mount whole hoard right from home server, and mounting it over the internet means that I need some kind of authentication.
Since I also use it at work, encryption is also nice, so I can always pass this bandwith as something work-friendly and really necessary, should it arouse any questions.
And while bandwith at work is pretty much unlimited, it's still controlled, so I wouldn't like to overuse it too much, and listening to oggs, mp3 and flacs for the whole work-day can generate traffic of 500-800 megs, and that's quite excessive to that end, in my own estimation.

The easiest way for me was trusty sshfs - it's got the best authentication, nice performance and encryption off-the-shelf with just one simple command. Problem here is the last aforementioned point - sshfs would generate as much bandwith as possible, caching content only temporarily in volatile RAM.

Persistent caching seem to be quite easy to implement in userspace with either fuse layer over network filesystem or something even simplier (and more hacky), like aufs and inotify, catching IN_OPEN events and pulling files in question to intermediate layer of fs-union.

Another thing I've considered was fs-cache in-kernel mechanism, which appeared in the main tree since around 2.6.30, but the bad thing about was that while being quite efficient, it only worked for NFS or AFS.
Second was clearly excessive for my purposes, and the first one I've come to hate for being extremely ureliable and limiting. In fact, NFS never gave me anything but trouble in the past, yet since I haven't found any decent implementations of the above ideas, I'd decided to give it (plus fs-cache) a try.
Setting up nfs server is no harder than sharing dir on windows - just write a line to /etc/exports and fire up nfs initscript. Since nfs4 seems superior than nfs in every way, I've used that version.
Trickier part is authentication. With nfs' "accept-all" auth model and kerberos being out of question, it has to be implemented on some transport layer in the middle.
Luckily, ssh is always there to provide a secure authenticated channel and nfs actually supports tcp these days. So the idea is to start nfs on localhost on server and use ssh tunnel to connecto to it from the client.

Setting up tunnel was quite straightforward, although I've put together a simple script to avoid re-typing the whole thing and to make sure there aren't any dead ssh processes laying around.

PID="/tmp/.$(basename $0).$(echo "$1.$2" | md5sum | cut -b-5)"
touch "$PID"
flock -n 3 3<"$PID" || exit 0
exec 3>"$PID"
( flock -n 3 || exit 0
  exec ssh\
   -qyTnN $3 -L "$1" "$2" ) &
echo $! >&3
exit 0

That way, ssh process is daemonized right away. Simple locking is also implemented, based on tunnel and ssh destination, so it might be put as a cronjob (just like "ssh_tunnel 2049: user@remote") to keep the link alive.

Then I've put a line like this to /etc/exports:

...and tried to "mount -t nfs4 localhost:/ /mnt/music" on the remote.
Guess what? "No such file or dir" error ;(
Ok, nfs3-way to "mount -t nfs4 localhost:/var/export/leech /mnt/music" doesn't work as well. No indication of why it is whatsoever.

Then it gets even better - "mount -t nfs localhost:/var/export/leech /mnt/music" actually works (locally, since nfs3 defaults to udp).
Completely useless errors and nothing on the issue in manpages was quite weird, but prehaps I haven't looked at it well enough.

Gotcha was in the fact that it wasn't allowed to mount nfs4 root, so tweaking exports file like this...


...and "mount -t nfs4 localhost:/music /mnt/music" actually solved the issue.

Why can't I use one-line exports and why the fuck it's not on the first (or any!) line of manpage escapes me completely, but at least it works now even from remote. Hallelujah.

Next thing is the cache layer. Luckily, it doesn't look as crappy as nfs and tying them together can be done with a single mount parameter. One extra thing needed, aside from the kernel part, here, is cachefilesd.
Strange thing it's not in gentoo portage yet (since it's kinda necessary for kernel mechanism and quite aged already), but there's an ebuild in b.g.o (now mirrored to my overlay, as well).
Setting it up is even simplier.
Config is well-documented and consists of five lines only, the only relevant of which is the path to fs-backend, oh, and the last one seem to need user_xattr support enabled.

fstab lines for me were these:

/dev/dump/nfscache /var/fscache ext4 user_xattr
localhost:/music /mnt/music nfs4 ro,nodev,noexec,intr,noauto,user,fsc

First two days got me 800+ megs in cache and from there it was even better bandwidth-wise, so, all-in-all, this nfs circus was worth it.

Another upside of nfs was that I could easily share it with workmates just by binding ssh tunnel endpoint to a non-local interface - all that's needed from them is to issue the mount command, although I didn't came to like to implementation any more than I did before.
Wonder if it's just me, but whatever...